1. Field of the Invention
The present invention relates to a fuel cell system including a fuel cell stack, a heat exchanger, a reformer, and a load applying mechanism provided in a casing.
2. Description of the Related Art
Typically, a solid oxide fuel cell (SOFC) employs an electrolyte of ion-conductive solid oxide such as stabilized zirconia. The electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly (unit cell). The electrolyte electrode assembly is interposed between separators (bipolar plates). In use, a predetermined number of the unit cells and the separators are stacked together to form a fuel cell stack.
In the fuel cell, an oxygen-containing gas or the air is supplied to the cathode. The oxygen in the oxygen-containing gas is ionized at the interface between the cathode and the electrolyte, and the oxygen ions (O2−) move toward the anode through the electrolyte. A fuel gas such as a hydrogen-containing gas or CO is supplied to the anode. Oxygen ions react with the hydrogen in the hydrogen-containing gas to produce water or react with CO to produce CO2. Electrons released in the reaction flow through an external circuit to the cathode, creating a DC electric energy.
For example, Japanese Patent Publication No. 6-24137 proposes to adopt a fuel cell in which the cell tightening surface pressure applied to respective cells can be set uniformly to a suitable value in order to achieve high performance and long life of the fuel cell. In the conventional technique, as shown in FIG. 13, the fuel cell includes a plurality of, e.g., three small stacks 1 disposed separately in a cell container 2.
Each of the small stacks 1 includes a cell stack 1a and cell tightening plates 1b provided on opposite sides of the cell stack 1a. Four tightening bolts 1c are inserted into the two upper and lower cell tightening plates 1b. Tightening nuts 1e are fitted to the respective tightening bolts 1c through tightening springs 1d to form the small stack 1. Further, the small stacks 1 are supported by three small stack support plates 3. Four support bolts 4 are inserted to the small stack support plates 3. Support nuts 5 are fitted to opposite ends of the support bolt 4.
However, in the conventional technique, since the four tightening bolts 1c are provided on the sides of the cell stack 1a of each small stack 1, the width of the small stack 1 in the direction perpendicular to the stacking direction of the small stack 1 is large.
Further, the small stack support plates 3 and the four support bolts 4 are provided for supporting the three small stacks 1, the space required for the entire fuel cell stack is considerably large. Accordingly, the size of the cell container 2 containing the fuel cell stack is large. Therefore, the space for the fuel cell stack is not utilized efficiently, and the heat capacity is large.